In conventional fuel cells containing hydrogen peroxide as the oxidizing agent, a metal anode is oxidized along with reduction of the hydrogen peroxide solution, causing an electric current to flow from the anode to the cathode through the electrolyte, which is contained within the hydrogen peroxide solution. An alternate method for utilization of hydrogen peroxide involves the decomposition of hydrogen peroxide to water and oxygen, wherein oxygen then acts as an oxidant in conventional fuel/oxygen fuel cells, such as the popular hydrogen/oxygen fuel cell; this method can be referred to as indirect hydrogen peroxide reduction.
However, in conventional liquid fuel cells containing H2O2, the aluminum anode oxidizes to aluminum oxides during reduction of the H2O2, resulting in significant deterioration of the fuel cell's performance over time due to poisoning of the metal surface of the anode. Moreover, selection of the cathode material is difficult, as only certain cathode materials will effectively reduce H2O2 at a desirable rate, i.e., at a rate of reduction which will produce sufficient current, but without undue H2O2 decomposition. Additionally, the direct reduction of hydrogen peroxide to water on the cathode surface is the rate-limiting reaction in the production of electricity from hydrogen peroxide, and thus a catalyst is required to achieve sufficient power density. Utilization of noble metal catalysts in this manner facilitates hydrogen peroxide decomposition, releasing oxygen as waste, and thus a decrease in cell efficiency.
Conventionally, noble metals, such as palladium and platinum, have been used as catalysts. Palladium and platinum, like all noble metals, however, are catalysts, not electrocatalysts, and as such will decompose to oxygen rapidly when placed in contact with hydrogen peroxide. This decomposition generates a great amount of heat, resulting in a large loss of efficiency, and thus requiring significantly more hydrogen peroxide to flow through the system than would be otherwise needed, to compensate for the energy lost through heat.
For example, as disclosed in prior U.S. Pat. No. 6,554,877, fuel cells using methanol as a liquid fuel, with a cathode made using screen-printing methods of 20% platinum on activated carbon on waterproof paper, have been used. However, as noted therein, catalyst poisoning or cathode sintering is encountered.
In prior U.S. Pat. No. 6,294,281, a fuel cell is disclosed having an anode and a cathode comprised of an enzyme, such as a dehydrogenase, organic compounds or organometallic molecules, which operate using fuels from biological systems. The '281 fuel cell, for example, is implanted into a portion of an animal or plant, and utilizes biological fluid, such as blood or sap, as the fuel, or may utilize tissue or cellulose outside of the biological organism. The '281 fuel cell is capable of reducing hydrogen peroxide at the cathode, but must first form the hydrogen peroxide in a non-enzyme-catalyzed electrode reaction or in an enzyme-catalyzed reaction on or off the cathode. Thus, the '281 fuel cell necessitates additional steps in the power generation process, and cannot be manufactured in an extremely compact design.
In view of the deficiencies of the above-mentioned conventional direct hydrogen peroxide and liquid fuel cells, it is an object of the present invention to provide a direct hydrogen peroxide fuel cell having an electrocatalyst not susceptible to catalyst poisoning or sintering, or side reactions with the oxidant. It is a further object of the present invention to provide a direct hydrogen peroxide fuel cell capable of stable power generation over time, i.e., which does not experience degradation over time. It is yet a further object of the present invention to provide a direct hydrogen peroxide fuel cell capable of being manufactured in a compact design, and which can run on liquid fuel and oxidant.